Since the first patents issued for sleeping bags in the 1930's, many improvements in sleeping bag design have been developed. Today, sleeping bags are made of extremely lightweight materials and provide substantially improved thermal insulation. In order to maximize the bag's thermal insulation capacity, mummy shaped bags have been developed to reduce the volume of air inside the bag, which enhances thermal efficiency because the user's body heat will be able to more efficiently warm a smaller volume of air. Another important improvement in sleeping bag design has been the development of the draft tube. A draft tube is a longitudinal insulation filled tube, which is attached to the inner lining of a sleeping bag and adjacent to the access zipper which is normally located on the side of the sleeping bag. The function of the draft tube is to overlay the inside surface of the zipper when the zipper is closed, so as to partially block the flow of warm air from the inside of the sleeping bag out through the zipper. The primary problem associated with mummy style sleeping bags is that while they are warmer than wider bags, they are relatively confining and uncomfortable. Wide bags, while more comfortable in warmer conditions, are by nature not as warm when the temperature drops such that the user may be uncomfortably cold. As a result, there is a need for a sleeping bag which essentially retains the thermal insulating benefits of a mummy style sleeping bag and draft tube, but is also comfortable and less confining during more moderate temperatures. The present invention satisfies that need.